Disparate mechanisms of antifolate resistance provoked by methotrexate and its metabolite 7-hydroxymethotrexate in leukemia cells: implications for efficacy of methotrexate therapy

Methotrexate (MTX) is one of the leading drugs in the treatment of leukemia, but extensive metabolism to 7-hydroxymethotrexate (7-OHMTX) can limit its therapeutic efficacy. In this study we investigated whether 7-OHMTX itself can provoke anti-folate resistance that may further disrupt MTX efficacy. For this purpose, we developed resistance to 7-OHMTX as well as MTX in 2 human leukemia cell lines (CCRF-CEM and MOLT-4) by stepwise exposure to increasing concentrations of 7-OHMTX and MTX. Consequently, both leukemia cell lines displayed marked levels of resistance to 7-OHMTX (> 10-fold) and MTX (> 75-fold). The underlying mechanism of resistance in the MTX-exposed cells was a marked decrease (> 10-fold) in reduced folate carrier (RFC)-mediated cellular uptake of MTX. This was associated with transcriptional silencing of the RFC gene in MTX-resistant CCRF-CEM cells. In contrast, the molecular basis for the resistance to 7-OHMTX was due solely to a marked decreased (> 95%) in folylpolyglutamate synthetase (FPGS) activity, which conferred more than 100-fold MTX resistance upon a short-term exposure to this drug. This is the first demonstration that 7-OHMTX can provoke distinct modalities of antifolate resistance compared with the parent drug MTX. The implications of this finding for MTX efficacy and strategies to circumvent MTX resistance are discussed.

[Ability of the tissues to assimilate glucose and the pyruvate and lactate levels after intravenous glucose load in patients with peripheral facial paralysis]

In 60 control subjects and 48 patients with peripheral facial nerve palsy carbohydrate metabolism was tested performing a rapid intravenous glucose tolerance test with 0.5 g glucose per 1 kg of actual body weight and with determination of concentrations of glucose, pyruvate and lactate at rest in fasting state and after intravenous glucose load. Glucose was determined in capillary blood by the orthotoluidine method, pyruvate and lactate in venous blood by the enzymatic method. In the group of patients with facial nerve palsy a significantly lower number of subjects had a normal ability of glucose assimilation by tissues and a significantly higher frequency of pathological results of glucose tolerance test with a high prevalence of fasting hyperglycaemia. In patients with abnormal glucose tolerance test the fasting pyruvate concentration was high. After an intravenous glucose load the concentration of pyruvate in the 120th minute of the test was significantly increased (p less than 0.05) in patients with facial nerve palsy independently of the degree of glucose tolerance impairment. In patients with pathological result of the glucose tolerance test disturbances were observed also in lactate concentration. The production of lactate was decreased in the initial phase and then it was increased in the time up to 120 minutes. No direct correlation was observed between the disturbances of pyruvate concentration and the preserved ability of glucose assimilation by the peripheral tissues.

Certain phosphate compounds in the erythrocytes of patients with primary hyperlipidaemia

The investigations were carried out in 30 patients with primary hyperlipidaemia (hypercholesterolaemia, hypertriglyceridaemia and mixed form). The serum total cholesterol and triglycerides, and in the erythrocytes the levels of AMP, ADP, ATP, ATP complex with Fe, MP, HDP and DGP were determined. Twenty blood donors served as a control group. The obtained results showed a statistically highly significant rise in ADP concentration in all investigated subgroups of hyperlipidaemic subjects, and a non-significant quantitative shift of other determined phosphate compounds.

[Activity of lactic dehydrogenase and its isoenzymes in cerebrospinal fluid in infantile cerebral palsy]

The observed group included 91 children aged from 2 to 15 years divided into two groups: I control--25 children, and II--66 children with severe infantile cerebral palsy. The following biochemical investigations were done in the cerebrospinal fluid: total LDH activity and total protein level before and after fluid condensation, and determination of LDH isoenzymes after condensation of fluid. In the group of children with absence of organic lesions of the central nervous system the mean total LDH activity was 17.6 mU/ml, this value was similar to that found by most authors. The isoenzyme pattern in the control group contained 3--4 fractions, the LDH4 fraction was, however, found in 2 cases only. In the group with infantile cerebral palsy the total LDH activity in the cerebrospinal fluid showed a considerable range of variations, its mean value was 32.7 mU/ml and was highly significantly above the mean value in controls. The LDH isoenzyme pattern in this group consisted of 4--5 LDH fractions with a fairly high proportion of cases with LDH4 and LDH5 fractions and with a high absolute activity of these fractions.